Tubes and cores are widely used in the film and paper industry for winding film and paper into roll form. These cores are usually made of paperboard and are formed by a spiral or convolute wrap process. Thus, one or more plies of paperboard are coated with adhesive and wrapped around a mandrel to seal each layer to the next in the structure. For lightweight uses, the tubes or cores are made of lightweight paperboard and may have only a few layers. However, for heavy duty uses, such as for winding and unwinding for newspaper and Rotogravure printing, the tubes are usually very long, for example up to about 10 ft. (3.08 m.) for U.S. Rotogravure printing and 10.5 ft. (3.22 m.), for European Rotogravure printing. In view of the large size, these tubes must be of very heavy or thick construction to be able to carry the weight of a large roll of paper.
In use on winding and unwinding equipment, the tubular cores are mounted on stub shafts or chucks of standard size. U-shaped metal end caps are typically inserted into the open ends of the tube to assist in more positive mounting of the paperboard cores on the chucks or stub shafts of the winding and unwinding equipment.
Many paperboard cores used in film and paper processes have a three-inch inside diameter. Similarly a substantial proportion of the commercially used printing and winding equipment has chucks and/or stub shafts designed to cooperate with three-inch inside diameter cores.
At times, printers and/or film and paper manufacturers prefer to use a larger tubular core on equipment designed for use with a core of smaller diameter in order to improve both vibration and dynamic strength performance. For example, many conventional cores have a six-inch inside diameter and it is clear that the use of a six-inch inside diameter core with equipment designed to support a core having a three-inch inside diameter can significantly impact vibration during the winding and unwinding process.
U.S. Pat. No. 4,875,636 to Kewin discloses a non-returnable newsprint carrier system in which the newsprint cylindrical core can be used without the need for metal end caps. The inside surfaces of the opposite end portions of the tubular core have substantially the same non-cylindrical configuration, profile and dimensions as the outside surfaces of the reel stub shafts of an offset printing press so that the tubular core and newsprint stub shaft will have a full profile fit in surface-to-surface contact over substantially the entire surface of the reel stub shafts inserted within the core during use thereof.
U.S. Pat. No. 4,874,139 to Kewin discloses tubular core assemblies which include an annular core insert member which may be made of a cellulosic material, permanently bonded to the inside end of a tubular paperboard core. The use of such an interior annular core insert can allow for the use of a smaller wall thickness paperboard tube. In practice, there is a problem with the annular core insert because it is fastened to the interior of the inside tube by an adhesive. The exterior of the core insert must have a tight fit with the interior of the core, inside the tube, to eliminate vibration and wobble in high speed winding and to try to keep the insert from breaking loose during sudden acceleration or deceleration of the unwind machine. Because of the relatively close tolerance fit between the annular core insert and the inside of the core, the adhesive, intended to bond the annular core insert to the core, is typically wiped out of the minimal space between the insert and the core during the axial insertion process. Moreover, unless the exterior surface of the annular core insert and the interior surface of the tube, are perfectly symmetrical and circular, gaps can be left between the two surfaces where no bonding occurs. Thus, in practice, the annular core inserts are seldom adhered securely to the tube and very seldom survive the winding operation, much less the unwinding operation.
The elimination of metal end caps for the mounting of cores on winding and unwinding equipment would be highly desirable. However, in practice the proposed systems of the prior art include various disadvantages as discussed above, including the poor bonding between interior annular core inserts and the ends of the tubular core and/or the need to reduce the diameter of inside portions of the tubular core in order to provide a tube with an inside surface having a profile matching the exterior profile of the reel stub shafts of winding and unwinding equipment. Moreover, there is no practical solution provided in the art for the recurring needs and desires of manufacturers to employ large diameter cores on equipment designed for use with smaller diameter cores.